Electrostatic conveyor

ABSTRACT

An electrostatic conveyor including a machine frame defining a feed table and a conveyor including a plurality of belts which move across the table to convey sheet material. The moving conveyor belts, along with charging members connected to the feed table, and the feed table itself define an electrostatic generator. The generator establishes an electrostatic field between sheets on the conveyor and the feed table. The field creates an electrostatic force which urges the sheets toward the table thereby frictionally engaging the sheets and the conveyor belts so that sheets are conveyed along the table by the belts.

0 United States Patent 1 3,690,646 Kolibas [45] Sept. 12, 1972ELECTROSTATIC CONVEYOR 2,572,765 11/ 1951 Roudaut ..3l0/7 [72] Inventor:hums A. K has B 3,351,340 11/1967 Levine ..271/51 Heights Ohio 3,495,8212/1970 Raterman ..271/51 [73] Assignee: Addressograph-Multigraph Cor-Primary Examiner-Joseph Wegbreit poration, Cleveland, OhioAttorney-Russell L. Root and Ray S. Pyle [22] Filed: July 8, 1970 [57]ABSTRACT Appl' 53053 An electrostatic conveyor including a machine framedefining a feed table and a conveyor including a plu- [52] US. Cl...271/45, 271/63 A, 271/75 rality 0f belts which move across the tableto convey [51] Int. Cl. ..B65h 5/02 Sheet material The moving Conveyorbelts along with [58] [Pi k] f Search n 45 51 3 10 7 charging membersconnected to the feed table, and the feed table itself define anelectrostatic generator. 5 References c The generator establishes anelectrostatic field between sheets on the conveyor and the feed table.UNITED STATES PATENTS The field creates an electrostatic force whichurges a the sheets toward the table thereby frictionally engagg g at Xing the sheets and the conveyor belts so that sheets are n e et a 71/45conveyed along the table y the belts. 2,410,611 ll/1946 Pratt et al...271/45 3,256,450 6/1966 Gartner ..3 10/6 15 Claims, 4 Drawing FiguresPATENTEUSEP 12 m2 JAN/E5 l0. KUL/BAS EY Q 3 Y Maw r Xm N 7 E 7 VS? W A 1ELECTROSTATIC CONVEYOR BACKGROUND OF THE INVENTION Field of theInvention The present invention relates to conveyors and moreparticularly relates to conveyors utilizing electrostatic forces topromote the conveyance of sheet or film-like articles.

Conveyors for sheet or film-like materials have been subject to severalmajor problems which have been related to the nature of the materialbeing conveyed, the conveying speeds which have sometimes been required,and the purpose and function of apparatus associated with the conveyors.

This invention has solved a severe problem wherein sheet material movedalong a flat plane by one conveyor, is transferred to a conveyor slopingupwardly at an angle that encourages slippage. However, the invention isapplicable to many sheetconveying situations.

Another example of an environment in which a sheet conveyorrnust operateat high speedunder demanding circumstances is found in an .on-line"printed sheet conveyor between a lithographic printing press and a sheetcollator.

In this environment, the conveyor must convey individual recentlyprinted sheets of paper, or the like, from the printing press to a givenpocket location in the collator at least at the rate at which sheets aredelivered from the press. Since the printing rate of lithographicpresses can be quite high, the associated conveyor must operate at ahigh enough speed that separation between successive sheets isadequately large for proper handling by the collating apparatus beingused. By operating the conveyor at a selected speed, the sheet spacingcan be maintained, decreased or increased.

In such an environment, there are a number of requirements which must bemet by the conveyor in order to perform in an optimum manner. Some ofthese are: (1) substantially positive engagement of the sheets with theconveyor; .(2) high conveying speeds; (3) avoidance of tracking ink onrecently printed sheets; and, (4) maintenance-of traction with, orcontrol of, sheets which are misaligned with the conveyor.

Positive engagement of sheets by the conveyor insures against sheetslippage and possible resultant reductions in the interval betweensuccessive sheets. In order to assure positive engagement, some meansfor establishing significant engagement forces between sheets and movingconveyor members must be employed.

High speed operation requires that the sheets be maintained on theconveyor by forces which are sufficiently large to overcome theaerodynamic lift exerted on the sheets. This lifting is created by theirspeed through the atmosphere surrounding the conveyor.

Sheets recently printed in a lithographic printing press bear ink imageswhich are moist. The ink on the sheets is subject to tracking whencontacted by elements of sheet handling apparatus such as a conveyor.Tracking occurs whenever the ink is smeared, deposited on a sheet at anunprinted location, or removed from a printed location on a sheet. Inorder to avoid tracking, sheets are usually conveyed by the apparatus insuch a way that relative movement between the sheets and sheetsupporting surfaces is avoided wherever possible. This requires that thesheets be positively driven or conveyed while avoiding contacting theprinting on the sheet.

Because of the structural characteristics of sheets of paper or similarfilm-like material, such articles are subject to misalignment onconveyors. The conveyor must be capable of maintaining control overmisaligned sheets as they are being conveyed. For optimum per formance,a conveyor should be constructed so that misalignment of sheets will notmaterially reduce the engagement forces between the conveyor andmisaligned sheet. If misalignment causes these forces to besignificantly reduced, aerodynamic lift-off, slipping and tracking canresult. This is particularly objectionable when an apparatus such as acollator is associated with the conveyor, since collator jamming is aptto occur if a sheet fed to it is not properly oriented.

The Prior Art Various proposals have been made to attempt to accomplishhigh speed paper. or film conveying with minimum ink tracking and.positive engagement of the material while maintaining control over thematerial even when misaligned. For example, it has been proposed toestablish pressure differentials across sheets and conveyor belts sothat the sheets are held in position on the conveyor belts bydifferential pressure forces. Ports are provided in the conveyor whichcommunicate with a source of subatmospheric pressure. When sheetsregister with these ports the pressure differential is established. Thepressure force holding the sheet on the conveyor is proportional to thenumber of ports the sheet registers with at any given time. Thisapparatus has operated reasonably well in avoiding tracking at highconveyor speeds except when conveyed sheets are misaligned with theconveyor.

When a sheet is misaligned with the conveyor, the sheet registers with arelatively small number of vacuum ports at any given time. This reducesthe total force tending to hold the sheet in engagement with theconveyor belts. Aerodynamic lift off of portions of the sheet thenoccurs. When part of a sheet lifts off the conveyor, the sheet can jamin associated apparatus. Tracking may also occur as a result of relativemovement between the sheet and the belts when the engagement forces arereduced.

Other sheet conveyor concepts employing rollers, grippers, etc. havebeen beset by tracking problems and speed limitations as well as bydifficulties arising from the presence of misaligned sheets in theapparatus.

Another problem which has affected some prior art conveyors and sheethandling apparatus has been that paper, film-like articles, etc.,frequently take on undesired electrostatic charges while being conveyed.These electrostatic charges frequently induce sufficiently largeelectrostatic forces acting on the material that the materials aredifficult to control or handle as desired in the apparatus.Electrostatic charges on such material in sheet form has also resultedin stacked sheets tightly clinging to each other. This frustratesfurther sheet handling operations. Therefore, the prior art hasattempted to minimize the build-up of electrostatic charges on paper orsimilar material by providing static discharge devices for dissipatingaccumulated charges on sheets.

Electrostatic forces have been intentionally produced in certain priorart sheet handling apparatus,

particularly where a sheet is to be held down against a member which isstationary with respect to the sheet. These electrostatic holdingdevices employ positive and negative electrical power supply electrodeseach of which is covered by a material having a relatively highelectrical resistance. The covered electrodes engage a sheet to be helddown at spaced locations thereby generating a small current in thesheet. The voltage drop across the material covering each electrodeproduces a large voltage difference between the sheet and eachelectrode. This produces a force for holding the sheet in position.

Aside from these static hold down devices, the prior art has principallyconcerned itself with elimination of electrostatic charges and forces inpaper or film handling equipment.

SUMMARY OF THE INVENTION The present invention provides a new andimproved material handling apparatus in the form of an electrostaticconveyor in which electrostatic charges are induced in material beinghandled. Electrostatic forces created by the charges are instrumental inmaintaining the moving material positively secured to the conveyor athigh conveying speeds regardless of expectable misalignment of thesheets and without tracking.

The new conveyor employs an article conveyor member which engages andmoves relative to a triboelectrically different member so that a chargeis created on the triboelectrical different member. The conveyor memberis electrically conductive transverse to its direction of movementrelative to the triboelectrically different member and non-conductive inthe direction of relative movement. When an article is placed on theconveyor member, charge is transferred to the article through theconveyor member transverse to its direction of relative movement. Thearticle is urged into frictional engagement with the conveyor memberwith electrostatic force so that the article is moved along with theconveyor member.

In a preferred embodiment, the new conveyor includes a plurality ofendless cloth belts which extend across a feed table. The conveyor beltsall move at the same speed and support sheets received from a suitablefeeder. The belts convey the sheets individually across the feed table.

The feed table itself is electrically grounded and a plurality ofnon-conductive, high triboelectrically negative charging strips areinterposed between the belts and the feed table. The belts and thecharging strips cooperate to form an electrostatic generator. Thecharging strips, because of their triboelectric property have anaffinity for the electrons in the associated conveyor belt. Thus, as thebelt moves across the charging strip, electrons are deposited on thecharging strip by the belt. This causes the surface of the chargingstrip engaging the belt to become negatively charged with respect to thegrounded feed table. This voltage level at the charging strip andconveyor belt interface is several kilovolts negative with respect tothe grounded feed table.

When a sheet is fed onto the conveyor belts, electric current isconducted from the charging strips transversely through the belts and tothe sheet. The sheet becomes highly negatively charged relative to thefeed table. The sheet is thus electrostatically attracted to the feedtable. Since the belts are between the sheet and the table, thisattraction urges the sheet toward the belts and causes the sheet tofrictionally hug the conveyor belts. Each sheet is driven across thefeed table by the belts as a result of the frictional engagement betweenthe sheets and belts.

The sheets and the belts are nearly at the same voltage level relativeto ground and accordingly the sheets are not electrostatically attractedto the belt. For this reason, the belts are spaced apart on the feedtable so that the sheets are attracted to the feed table betweenadjacent belts. The sheets are thus urged uniformly into engagement witheach belt.

The charging strips are preferably composed of polytetrafluoroethylene,a product sold commercially by E. I. Dupont under the trademark TEFLON.This material has an extremely high resistance to electrical currentflow, is non-conductive, is triboelectrically negative with-respect tomost other materials, and has a sufficiently low surface energy thatforeign matter does not adhere to its surface.

The belts are approximately neutral on the triboelectric scale and arepreferably woven from fibrous material having a relatively highelectrical resistivity. The belts have an extremely high electricalresistance measured in the plane of the belt; however since the beltsare thin, the electrical resistance measured through their thickness isnot extremely large even though the resistivity of the belt material ishigh. This enables current to be conducted through the belts to sheetsriding on them.

A conveyor constructed in accordance with the present inventionmaintains a sheet in frictional contact with each individual belt. Wherethe printed image on a sheet being conveyed is facing the belts, theimage is not tracked because of the nap, or fibrous nature of thesurface of the belts.

Since the charge on the sheet is distributed across the entire face ofthe sheet, the sheet is maintained in frictional engagement with eachconveyor belt regardless of the orientation of the sheet with respect tothe belt. Hence, misalignment of the sheet with respect to its directionof travel through the conveyor does not adversely effect conveyance ofthe sheet.

As a sheet moves from the conveyor, the charge on the sheet issubstantially dissipated by a low energy are to the grounded feed table.Even when stacked, sheets which have been conveyed by this new conveyordo not carry sufficient residual charges to cause them to cling tightlytogether.

A principal object of the present invention is the provision of a newand improved sheet conveyor mechanism utilizing electrostatic forces inconveying sheets.

Other objects and advantages of the present invention should becomeapparent from the following detailed description thereof made withreference to the accompanying drawings which form part of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side elevationalview of a conveyor embodying the present invention;

- FIG. 2 isa cross sectional view seen from the plane indicatedby theline 2-2 of FIG. 1; I I

FIG. 3 is a schematic view of a portion of the apparatus shown in FIG.1;

FIG. 4 is a fragmentary view of one belt land area of thoseshown in FIG.2, on a scale which is larger than the scale of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT or other sheet handling device.

The apparatus includes a machine frame 12 supporting a conveyorbed 14. Aconveyor, generally designated at 16, isassociated with the conveyor bed14 for conveying sheets 17 in the direction shownby the arrows inFIG. 1. e I a The conveyor '16 includes pulleys 18, 20 supportedat'opposite ends .of the conveyorbed. Sheets 17 are transported on thesurface of endless belts 22 trained around the pulleys 18, 20. Belts 22have upper reaches extending along the bed. A variable speed electricmotor 24 drives the pulley 18 so that the belts 22 are positively drivenacross the conveyor bed 14. In the preferred and illustrated embodimentof the invention seven belts 22 are employed in the conveyor.

The conveyor bed 14 includes a plate 32 (FIG. 2) formed by an aluminumextrusion defining seven spaced, parallel lands 34 projecting upwardlyfrom the plate. The. lands 34 define flatbottomed recesses 36 betweenthem. The lands and recesses extendalong the conveyor bed parallelingpath of travel of the conveyed sheets 17. Preferably the lateral sidesof the plate are formed by recessed portions 37 (FIG. 2). The upperreach of each belt 22 rides on a land 34. Each land has substantiallythe same width as the associated belt. Generically, the plate and itsland area may be termed as a bed member. Usually the bed will actuallysupport the belts against gravity, but not necessarily so. For example,the bed may be vertical.

An electrical heating element 40 is attached to the lower face of thefeed table. The element 40 is energized to heat the plate from anelectrical power supply through a suitable thermostatic control 42 (FIG.1). The control 42 governs energization of the element 40 to'maintainthe plate 32 at a predetermined desired temperature. l-Ieat from theplate is transferred to the belts in order to maintain the belts at aminimum desired dryness level. This assures that the electricalresistivity of the belts is not reduced as a function of humidity in theair ambient the apparatus.

Charging members 44 are disposed atop the lands 34 and eachis-interposed between a belt and its associated land. The chargingmembers 44 are continuous strips of dielectric material. These areattached to the lands by an adhesive and extend the length of the table.

The belts 22, charging members 44 and plate 32 form an electrostaticgenerator which is generally designated at 50 (FIG. 3). The generator 50produces electrostatic charges and concomitant electrostatic forces formaintaining sheets on the conveyor as the sheets advance. As shown inFIG. 3, the pulleys 18,20 and plate 32 are electrically grounded as isthe machine frame 12. The belts 22 are driven about the pulley 18, 20with the upper reaches contacting the associated charging members 44. 1

Each belt 22 is constructed of material characterized by having a highelectrical resistivity and relative neutrality on the triboelectricscale. In one conveyor which was successfully operated, the belts werestitched, two-ply cotton fabric 1 inch wide and 0.030 inch thick. Atypical volume electricalresistivity for this material is about 10ohm/cm. Becauseof the relatively high resistivity of the cottonmaterial, the belts have an extremely high electricalresistance-measured in the plane of thebelt. However, because the beltsare thin, the electrical resistance measured transverselyof the plane ofthe belts is not extremely large. The plate heater 40 prevents the beltsfrom picking up moisture in the atmosphere which could otherwise reducethe resistivity of the belt material. This cotton material is relativelyneutral in the triboelectric series; thatis, the material has no more ofa propensity for giving up electrons than for accepting electrons.

The surfaces of these belts are irregular, because of the projectingends of the woven cotton fibers, and produces a soft nap. The nap on theupper surface of thebelts enables each belt to engagerecently printedsheets over an extremely large number of small area locations. This typeof engagement avoids ink transfer and thus materially reduces anytendency toward tracking.

The charging members 44 are preferably strips ofpolytetrafluoroethylen'e (TFE), a plastic material sometimes known bythe trademark TEFLON. TFE is triboelectrically different from thecottonbelt material and is close to the negative end of the triboelectricseries. Thus when nearly any other material, including cotton, is rubbedon the TFE, the TFE material picks up electrons from the other material.

In addition to having a strong affinity for electrons, the T FE has anextremely high electrical resistivity (about 10 ohm/cm). Thus, electronsdeposited on the TFE are not conducted away from the TFE-belt interfacethrough the TFE. Hence, the TFE tends to become electrically chargednegative with respect to ground when the belts are moved.

The TFE is also advantageous for use as a charging member since dirt orother contaminants do not adhere to its surface. Even when foreignsubstances are disposed on the surface of the TFE, its affinity forelectrons is not materially diminished as a result of the presence ofthe contaminants.

Because the TFE members 44 have an affinity for electrons when rubbed bythe cotton belts, and due to the negative charge taken on by the TFE asthe conveyor operates, the members 44 are, for convenience, referred tohereinafter as charging members.

As each belt 22 moves across its associated charging member 44,electrons are deposited by the belt on the associated charging member.Since the charging members 44 are nonconductive, the electrons remain onthe surface 44a (FIG. 4) of the charging member 44 and the memberbecomes charged negative with respect to ground. Although electrons areconstantly deposited on the charging members 44 as the belts move, thenegative charge is maintained at a relatively constant peak level. Whenthe peak level is reached, electrons are dissipated from the chargingmembers 44 by are discharges from the edges of the charging members 44to the grounded conveyor bed 14 at the same rate elecconstruction, thecharging members are 0.01 inches thick and are chargedto about 7kilovolts negative with, respect to the voltage level of the feed table.The

thickness of the TF E can be increased or decreased to respectivelyincrease or decrease the charge level.

I The charge relationship between the variouselements of thegenerator50are shown schematically in FIG. 4. Itwillbe noted that the belt-chargingmember interface is negative on the charging member face and positiveatthe belt face. This charge relationship causes each belt to cling to itsassociated charging member whenever the belt moves relative to thecharging member. Hence belt tensioning mechanisms are not required formaintaining the belts in contact with the charging members. Moreoverbecause the belts cling to the charging members the conveyor can beoriented as desired without altering its performance. For example, theconveyor can be inverted or inclined from its orientation shown inFIG. 1. I

When a sheet of paper is introduced onto the conveyor belts, electronsare conducted through the belts from the charging members 44transversely of the plane of the belts and to the paper. The paper issomewhat conductive and hence the entire surface of the paper facing thefeed table becomes charged to a relatively large negative voltage withrespect to the feed table. This charge distribution is shownschematically in F IG. 4. The sheet does not have a large capacity forelectrons and hence becomes negatively charged, as described, as aresult of a current flow which is not sufficiently large to dissipatecharge from the members 44.

It should be noted that paper which has recently been printed in alithographic type printing press is sufficiently moist that the surfaceof the paper is sufficiently electrically conductive to receiveelectrons from the charging members. Electrically conductive materials,and paper or plastic film having conductive coatings are also readilyconveyed by the new conveyor. Where paper is not sufficiently moist tobe advanced by the conveyor, the humidity ambient the conveyor or feederassociated with it should be increased to produce adequate conductivityof the paper.

The portions of the sheet which overlie the recesses 36 in the feedtable are electrostatically attracted to the feed table across an airgap 55 between the sheet and the bottom of each recess 36. When lightweight paper is conveyed, these portions are apt to dish as shown at 60(FIG. 4). The recesses 36 are sufficiently deep that the dished portions60 will not engage the bottoms of 8 the recesses and discharge thesheet. Air is a dielectric, but a solid dielectric may be used toprevent sheet sag if needed.

The electrostatic force of attraction between the sheet and bottom ofthe recesses causes the sheet to be urged into frictional engagementwith the belts so that the belts positively convey the sheet as theelectrostatic force maintains the sheet in contact with the belts. inpractice it has been found that the lands, charging members 44 and beltsshould be greater than one half inch widein order to produce suitablylarge electrostatic frictional forces between the sheet and theconveyor. Preferably the belt, lands and charging members 44 are about 1inch wide and the recesses 36 about three-eighths inch wide. It has alsobeen found that the belts should move relative to the charging membersat least at 25 inches per second for optimum generation of electrostaticforces.

When the sheet 17 moves off the end of the conveyor unit, the distancebetween the feed table and the sheet increases substantially resultingin an extremely high voltageacross the now enlarged air gap betweenthesheet and the feedtable. When this occurs, the charge on the sheet isdissipated by a low' energy are established between the grounded machineframe and the sheet. Thereafter, the sheet is substantially uncharged,or at least is sufficiently slightly charged that when stacked withother similar sheets each sheet is relatively easily removed from thestack.

What is claimed is:

l. A conveyor for articles comprising:

a support bed having a bed surface;

a conveyor assembly comprising at least one conveyor member supportedfor movement on a path of travel across at least a portion of said bedsurface;

said conveyor member having a first surface oriented toward said bed anda second'obverse article transport surface facing away from the bed;and,

charge means for establishing a first charge level between said bed andsaid first surface and a second charge level between said second surfaceand an article thereon, said first and second charge levels beingunequal and producing an electrostatic force urging said article towardsaid bed and into frictional engagement with said conveyor member tocause said conveyor member to advance an article across said bed.

2. A conveyor as claimed in claim 1 wherein said charge means iscomprised of an electrostatic generator formed by said at least oneconveyor member and a nonconductive charging member interposed betweenand contacting said bed surface and said conveyor member, said conveyormember and said nonconductive charging member movable relative to eachother and being triboelectrically different.

3. A conveyor as claimed in claim 2 wherein said conveyor membercomprises a flat belt member having a low resistance to electric currentflow transversely to the plane of said belt as compared to theelectrical resistance of the belt in its plane.

4. A conveyor for articles comprising:

a support bed having a bed surface; 1

a conveyor assembly comprising at least one conveyor member comprising aflat belt supported for movement on a path of travel across tion of saidbed surface;

said conveyor member having a first surface oriented toward said bed andan obverse article transport surface facing away from the bed; and,

charge means for establishing a charge acrosssaid article transportsurface and said bed whereby as article placed on said article transportsurface substantially assumes the charge level of said article transportsurface and an electrostatic force urges said article toward said bedand into frictional engagement with said conveyor member to cause saidconveyor member to advance an article across said bed;

said charge means comprising an electrostatic generator formed by saidat least one conveyor member and anonconductive charging memberinterposed between said bed surfaceand said conveyor member, saidcharging member contacting said bed surface and defining a surfaceengageable with said belt;

said conveyor member and said nonconductive charging member movablerelative to each other and ,said charging member surface'formed by amaterial which is triboelectrically negative with respect to the beltand has a low surface energy whereby electrons are deposited on saidcharging member surface by said belt and said charging at least apormember surface resists adhesion of foreign matter. 3

5. A conveyor as claimed in claim 4 wherein said belt member iscomprised of a woven fibrous material which is about neutral on thetriboelectric scale.

6. A conveyor as claimed in claim 2 wherein said bed surface iselectrically grounded whereby an electrostatic charge is created acrosssaid charging member and said bed surface. r

7. A conveyor for articles comprising:

a support bed having a bed surface;

a conveyor assembly comprising at least one conveyor member comprising aflat endless belt supported for movement on a path of travel across atleast a portion of said bed surface;

said conveyor member having a first surface oriented toward said bed andan obverse article transport surface facing away from the bed; and,

charge means for establishing a charge across said article transportsurface and said bed whereby an article placed on said article transportsurface substantially assumes the charge level of said article transportsurface and an electrostatic force urges said article toward said bedand into frictional engagement with said conveyor member to cause saidconveyor member to advance an article across said bed; i

said charge means comprising an electrostatic generator formed by saidat least one conveyor member and a nonconductive charging memberinterposed between and contacting said bed surface and said conveyormember, said conveyor member and said nonconductive charging membermovable relative to each other and being triboelectrically different;

said belt having a low resistance to electric current flow through itsthickness as compared'to its electrical resistance in its plane andeffective to consupport said support member at spaced apart locations;drive means for moving said belts relative to said support member;

a plurality of coextending generally parallel charging members attachedto said support member and extending along said support member at spacedapart locations, each belt overlying and coextending with a respectiveone of said charging members whereby each belt slidingly contacts itsassociated charging member when said belt moves along said supportmember;

each of saidibelts comprised of material having a high electricalresistance parallel to said charging member and a relatively lowresistance transverse to said charging member; and,

each of said charging members being triboelectrically different from itsassociated belt;

. 9. Apparatus as claimed in claim 8 wherein said belts 0 and saidcharging members are no less than about onehalf inch wide, and furtherincluding structure provid* ing a dielectric material between adjacentbelts, said dielectric material interposed between adjacent belts, saiddielectric material interposed between conveyed material bridging saidbelts and said support member.

10. Apparatus as claimed in claim 9 wherein said structure includes aplurality of recesses formed in said support member between said belts,said recesses defining a space between conveyed material on said beltsand said support member, said dielectric material comprising air in saidspace.

11. Apparatus as claimed in claim 8 wherein. said belts are formed froma woven fabric material having a high electrical resistivity and saidcharging members are defined by thin strips of material characterized byhaving an extremely high electrical resistivity and beingtriboelectrically negative with respect to the belt material.

12. Apparatus as claimed in claim 11 wherein said charging members arecomposed at least principally of polytetrafluoroethylene.

13. Apparatus as claimed in claim 8 and further including heater meansfor heating said belts to a predetermined temperature whereby to limitthe moisture content of said belts and control their electricalresistivity.

14. A method of conveying articles comprising:

providing a conveyor bed;

supporting a conveyor belt along the bed;

moving the conveyor belt relative to the bed;

placing an article on an article engaging surface of the conveyor belt;

electrically insulating the article from the bed;

establishing a charge across the article and bed while maintaining thearticle and the article engaging surface of the conveyor belt atsubstantially the generally parallel endless belts extending along callyinsulating the belt from the bed comprises interposing a nonconductivecharging member between said belt and said bed and establishing a chargeacross the article and bed comprises engaging the belt with a surface ofthe charging member as the belt moves relative to the charging memberand creating a charge across the charging member surface and the bed.

1. A conveyor for articles comprising: a support bed having a bedsurface; a conveyor assembly comprising at least one conveyor membersupported for movement on a path of travel across at least a portion ofsaid bed surface; said conveyor member having a first surface orientedtoward said bed and a second obverse article transport surface facingaway from the bed; and, charge means for establishing a first chargelevel between said bed and said first surface and a second charge levelbetween said second surface and an article thereon, said first andsecond charge levels being unequal and producing an electrostatic forceurging said article toward said bed and into frictional engagement withsaid conveyor member to cause said conveyor member to advance an articleacross said bed.
 2. A conveyor as claimed in claim 1 wherein said chargemeans is comprised of an electrostatic generator formed by said at leastone conveyor member and a nonconductive charging member interposedbetween and contacting said bed surface and said conveyor member, saidconveyor member and said nonconductive charging member movable relativeto each other and being triboelectrically different.
 3. A conveyor asclaimed in claim 2 wherein said conveyor member comprises a flat beltmember having a low resistance to electric current flow transversely tothe plane of said belt as compared to the electrical resistance of thebelt in its plane.
 4. A conveyor for articles comprising: a support bedhaving a bed surface; a conveyor assembly comprising at least oneconveyor member comprising a flat belt supported for movement on a pathof travel across at least a portion of said bed surface; said conveyormember having a first surface oriented toward said bed and an obversearticle transport surface facing away from the bed; and, charge meansfor establishing a charge across said article transport surface and saidbed whereby as article placed on said article transport surfacesubstantially assumes the charge level of said article transpoRt surfaceand an electrostatic force urges said article toward said bed and intofrictional engagement with said conveyor member to cause said conveyormember to advance an article across said bed; said charge meanscomprising an electrostatic generator formed by said at least oneconveyor member and a nonconductive charging member interposed betweensaid bed surface and said conveyor member, said charging membercontacting said bed surface and defining a surface engageable with saidbelt; said conveyor member and said nonconductive charging membermovable relative to each other and said charging member surface formedby a material which is triboelectrically negative with respect to thebelt and has a low surface energy whereby electrons are deposited onsaid charging member surface by said belt and said charging membersurface resists adhesion of foreign matter.
 5. A conveyor as claimed inclaim 4 wherein said belt member is comprised of a woven fibrousmaterial which is about neutral on the triboelectric scale.
 6. Aconveyor as claimed in claim 2 wherein said bed surface is electricallygrounded whereby an electrostatic charge is created across said chargingmember and said bed surface.
 7. A conveyor for articles comprising: asupport bed having a bed surface; a conveyor assembly comprising atleast one conveyor member comprising a flat endless belt supported formovement on a path of travel across at least a portion of said bedsurface; said conveyor member having a first surface oriented towardsaid bed and an obverse article transport surface facing away from thebed; and, charge means for establishing a charge across said articletransport surface and said bed whereby an article placed on said articletransport surface substantially assumes the charge level of said articletransport surface and an electrostatic force urges said article towardsaid bed and into frictional engagement with said conveyor member tocause said conveyor member to advance an article across said bed; saidcharge means comprising an electrostatic generator formed by said atleast one conveyor member and a nonconductive charging member interposedbetween and contacting said bed surface and said conveyor member, saidconveyor member and said nonconductive charging member movable relativeto each other and being triboelectrically different; said belt having alow resistance to electric current flow through its thickness ascompared to its electrical resistance in its plane and effective toconduct current to an article on said article transport surface fromsaid charging member whereby an article is charged relative to said bedsurface and electrostatically attracted to said bed surface.
 8. Anelectrostatic conveyor apparatus for sheet or film-like materialcomprising: an electrically grounded conductive support member; aconveyor comprising a plurality of coextending generally parallelendless belts extending along said support member at spaced apartlocations; drive means for moving said belts relative to said supportmember; a plurality of coextending generally parallel charging membersattached to said support member and extending along said support memberat spaced apart locations, each belt overlying and coextending with arespective one of said charging members whereby each belt slidinglycontacts its associated charging member when said belt moves along saidsupport member; each of said belts comprised of material having a highelectrical resistance parallel to said charging member and a relativelylow resistance transverse to said charging member; and, each of saidcharging members being triboelectrically different from its associatedbelt.
 9. Apparatus as claimed in claim 8 wherein said belts and saidcharging members are no less than about one-half inch wide, and furtherincluding structure providing a dielectric material between adjacentbelts, said dielectric material interposed between adjacent belts, saiddielectRic material interposed between conveyed material bridging saidbelts and said support member.
 10. Apparatus as claimed in claim 9wherein said structure includes a plurality of recesses formed in saidsupport member between said belts, said recesses defining a spacebetween conveyed material on said belts and said support member, saiddielectric material comprising air in said space.
 11. Apparatus asclaimed in claim 8 wherein said belts are formed from a woven fabricmaterial having a high electrical resistivity and said charging membersare defined by thin strips of material characterized by having anextremely high electrical resistivity and being triboelectricallynegative with respect to the belt material.
 12. Apparatus as claimed inclaim 11 wherein said charging members are composed at least principallyof polytetrafluoroethylene.
 13. Apparatus as claimed in claim 8 andfurther including heater means for heating said belts to a predeterminedtemperature whereby to limit the moisture content of said belts andcontrol their electrical resistivity.
 14. A method of conveying articlescomprising: providing a conveyor bed; supporting a conveyor belt alongthe bed; moving the conveyor belt relative to the bed; placing anarticle on an article engaging surface of the conveyor belt;electrically insulating the article from the bed; establishing a chargeacross the article and bed while maintaining the article and the articleengaging surface of the conveyor belt at substantially the same chargelevel to substantially prevent electrostatic attraction between thearticle and the article engaging surface of the conveyor belt;attracting the article toward the bed by said charge to establish africtional conveying force between the article and the article engagingsurface; and, conveying the article with the belt relative to the bed.15. A method as claimed in claim 14 wherein electrically insulating thebelt from the bed comprises interposing a nonconductive charging memberbetween said belt and said bed and establishing a charge across thearticle and bed comprises engaging the belt with a surface of thecharging member as the belt moves relative to the charging member andcreating a charge across the charging member surface and the bed.